The endotracheal tube is an artificial airway device usually made of plastics or rubber material which consists of a flexible, usually somewhat curved tube, typically of 8-mm internal diameter in adults, with a square-cut outer or proximal end for attachment to a standard 15-mm connector and a bevelled or diagonally-cut opposite or distal end for ease of insertion through the laryngeal aperture (glottis) and into the trachea (windpipe). Normally, an endotracheal tube has hermetically sealed engagement to the walls of the trachea, by reason of a typically cylindrical or spheroidal concentric plastic or rubber cuff fitted to the tube shaft, at some 2 to 3 cm of proximal offset from said bevelled end. Such a cuff is inflated by means of an inflating syringe via an inflation line commonly running in the wall of said tube and continuous with a flexible pilot tube, pilot balloon and spring-loaded check valve; after the endotracheal tube has been installed to the correct depth in the patient's trachea, the cuff is inflated, and the check valve retains the cuff in its inflated state.
A wide variety of such endotracheal tubes are known and in common use throughout the world, and most have in common the features detailed above. Their popularity is due to their ability to provide means of administering anaesthetic gases to the patient's lungs while simultaneously preventing entry into the lungs of potentially lethal gastric juice which may otherwise flood into the airways when the body's protective reflexes have been abolished by the administration of general anaesthesia. However, many complications are known to be caused by the placement of such tubes, whether from trauma of insertion, pressure of the tube lying against the walls of the larynx or pressure exerted on the delicate walls of the trachea by the sealing cuff once inflated. The traditional bevel on an endotracheal tube is in no way designed to fit the slot-shaped and somewhat triangular aperture it must pass through when the tube is inserted, resulting commonly in injury to the larynx due to the bevel tip bruising one or the other side of the larynx during passage. Also, once installed, the circular cross-section of conventional tubes differs from the roughly triangular slotted shape of the laryngeal aperture so that when the vocal cords forming the sidewalls of said triangle contract against this circular shape, stretching and consequent malfunction of the cords commonly occurs. Tubes have been designed, for example some designs of plastic (PVC) tube manufactured by Mallinkrodt (Germany and U.S.A.) in which the bevelled tip is directed away from the tube's side wall, but such tube-bevel design does not bring the leading edge of the bevel into the mid-line of the tube shaft, and the tube is of uniform hardness (typically 80 durometer).
To insert an endotracheal tube in a patient's windpipe, an instrument called a laryngoscope is normally used. This device comprises a light source placed within a blade designed to lift the tongue forwards, revealing the glottic aperture below the posterior surface of the tongue. Endotracheal tubes are normally curved so as to facilitate entry of the bevelled tube tip between the vocal cords once these have been revealed by the laryngoscope. However, this curvature of the tube, while facilitating entry into the glottis, actually causes the tube to scrape against the anterior wall of the windpipe as it passes further into place, because the anatomy of the windpipe curves in the direction opposite to the curvature of the tube. My pending patent application Ser. No. 08/901,055 describes an intubating laryngeal mask, namely, an LMA modified to act as a guide to installing an endotracheal tube; wherein the need to use a laryngoscope can be avoided, while also avoiding the need for the endotracheal tube to be curved. The present invention pertains to an endotracheal tube designed principally for use with an intubating LMA, and the disclosure of said pending patent application is hereby incorporated by reference.